Fuel injection system of internal combustion engine

ABSTRACT

An internal combustion engine provided with a common rail ( 13 ) and fuel injectors ( 3 ) connected to the common rail ( 13 ). When pilot injection is performed, the injection pressure pulsates. At this time, the injection amount of the main injection fluctuates by a certain fluctuation pattern. If indicating on an abscissa a time interval from when pilot injection is started to when main injection is started and indicating on the ordinate a fluctuation amount of main injection, the fluctuation pattern of the injection amount of the main injection becomes a form contracted or expanded in the abscissa direction and ordinate direction in accordance with the rail pressure. This characteristic is utilized to find the fluctuation amount of the injection amount of the main injection.

TECHNICAL FIELD

The present invention relates to a fuel injection system of an internalcombustion engine.

BACKGROUND ART

An internal combustion engine designed so that the nozzle chambers offuel injectors are connected to a common rail through high pressurelines and performing two fuel injections, for example a pilot injectionand a succeeding main injection, is known (for example, see JapaneseUnexamined Patent Publication (Kokai) No. 2000-18074).

When using such a common rail, however, when fuel injection isperformed, the pressure wave generated in a nozzle chamber of a fuelinjector at that time propagates through the high pressure line andreaches the common rail. Next, this pressure wave proceeds in the highpressure rail toward the nozzle chamber. This causes violent pulsationof the fuel pressure in the nozzle chamber.

In this conventional internal combustion engine, the main injection isperformed after the pilot injection when this violent pulsation of thefuel pressure occurs in the nozzle chamber due to the reflected wave inthe common rail. If performing the main injection when the fuel pressurein the nozzle chamber violently pulsates in this way, however, theproblem arises that the injection amount of the main injection greatlyfluctuates and ends up greatly deviating from the normal amount.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a fuel injection systemof an internal combustion engine able to accurately control theinjection amount to the target value even when using a common rail.

According to the present invention, there is provided a fuel injectionsystem of an internal combustion engine provided with a common rail andfuel injectors connected to the common rail, performing fuel injectionfrom each fuel injector at least the two times of prior injection andlater injection during one cycle of the engine, and changing influctuation amount of the later injection with respect to a target valuedepending on a time interval from when the prior injection is performedto when the later injection is performed, the fuel injection system ofan internal combustion engine provided with a storage device for storinga reference fluctuation amount of the later injection changing alongwith a reference fluctuation pattern along with an increase in the timeinterval when the rail pressure is a predetermined reference railpressure and storing a contraction rate or expansion rate of thefluctuation pattern when contracting or expanding the fluctuationpattern of the fluctuation amount of the later injection when the railpressure is not the reference rail pressure to overlay it on thereference fluctuation pattern, a calculation device for using thecontraction rate or expansion rate to calculate the fluctuation amountof the later injection in accordance with the rail pressure from thereference fluctuation amount and time interval, and a control device forusing the fluctuation amount calculated by the calculation device tocontrol an injection amount to a target value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overview of a compression ignition type internal combustionengine;

FIG. 2 is a side sectional view of a tip of a fuel injector;

FIGS. 3A and 3B are views of injection patterns;

FIGS. 4A and 4B are views of maps of injection amounts;

FIGS. 5A and 5B are views of maps of main injection timing etc.;

FIGS. 6A to 6C are views of fluctuation amounts of main injection;

FIGS. 7A to 7C are views of fluctuation amounts of main injection;

FIGS. 8A and 8B are views of fluctuation amounts of main injection;

FIG. 9 is a flow chart of fuel injection control;

FIGS. 10A to 10D are views of contraction rates or expansion rates;

FIGS. 11A to 11C are views of fluctuation amounts of valve openingtiming of a needle valve;

FIGS. 12A and 12B are views of fluctuation amounts of main injection;

FIGS. 13 and 14 are flow charts of fuel injection control;

FIGS. 15A to 15C are views of contraction rates or expansion rates;

FIGS. 16A to 16D are views of contraction rates or expansion rates; and

FIGS. 17 and 18 are flow charts of fuel injection control.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, 1 is a compression ignition type internalcombustion engine body, 2 a combustion chamber of a cylinder, 3 a fuelinjector for injecting fuel into a combustion chamber 2, 4 an intakemanifold, and 5 an exhaust manifold. The intake manifold 4 is connectedthrough an intake duct 6 to an outlet of a compressor 7 a of an exhaustturbocharger 7. The inlet of the compressor 7 a is connected to an aircleaner 8. The intake duct 6 has arranged inside it a throttle valve 9driven by a step motor. On the other hand, the exhaust manifold 5 isconnected to an inlet of an exhaust turbine 7 b of the exhaustturbocharger 7.

The exhaust manifold 5 and the intake manifold 4 are connected to eachother through an exhaust gas recirculation (hereinafter referred to asan “EGR”) passage 10. The EGR passage 10 has an electronic control typeEGR control valve 11 arranged in it. On the other hand, each fuelinjector 3 is connected through a fuel feed line 12 to a common rail 13.The common rail 13 is supplied inside it with fuel from a fuel tank 15by an electronic control type variable discharge fuel pump 14. The fuelsupplied to the common rail 13 is supplied through the fuel feed lines12 to the fuel injectors 3. The common rail 13 is provided with a fuelpressure sensor 16 for detecting the fuel pressure in the common rail13. Based on the output signal of the fuel pressure sensor 16, thedischarge of the fuel pump 14 is controlled so that the fuel pressure inthe common rail 16 becomes the target fuel pressure.

An electronic control unit 20 is comprised of a digital computer and isprovided with a ROM (read only memory) 22, RAM (random access memory)23, CPU (microprocessor) 24, input port 25, and output port 26 allconnected by a bidirectional bus 21. The output signal of the fuelpressure sensor 16 is input through a corresponding AD converter 27 tothe input port 25. On the other hand, an accelerator pedal 17 has a loadsensor 18 connected to it to generate an output voltage proportional tothe depression L of the accelerator pedal 17. The output voltage of theload sensor 18 is input through the corresponding AD converter 27 to theinput port 25. Further, the input port 25 has a crank angle sensor 19connected to it for generating an output pulse every time a crankshaftrotates by for example 15°. On the other hand, the output port 26 hasconnected to it the fuel injectors 3, a step motor for driving thethrottle valve 9, the EGR control valve 11, and the fuel pump 14 throughcorresponding drive circuits 28.

FIG. 2 is an enlarged view of a fuel injector 3. As shown in FIG. 2, thefuel injector 3 is provided with a needle valve 31 able to sit on avalve seat 30, a suck chamber 32 formed around a tip of the needle valve31, an injection port 33 extending from the suck chamber 32 to theinside of the combustion chamber 2, and a nozzle chamber 34 formedaround the needle valve 31. The nozzle chamber 34 is connected to thecommon rail 13 through a high pressure fuel feed passage extendingthrough the inside of the body of the fuel injector 3 and the inside ofthe fuel feed line 12, that is, the “high pressure line 35”. The highpressure fuel in the common rail 13 is supplied through the highpressure line 35 to the inside of the nozzle chamber 34.

The fuel injector is formed inside it with a pressure control chamber 36facing the back surface of the needle valve 31. The pressure controlchamber 36 is provided inside it with a compression spring 37 pressingthe needle valve 31 toward the valve seat 30. The pressure controlchamber 36 is connected on the one hand through an inlet sideconstriction 38 to the middle of the high pressure line 35 and on theother hand through an outlet side constriction 39 to a fuel overflowport 41 controlled to open and close by an overflow control valve 40.The pressure control chamber 36 is continuously supplied with highpressure fuel through the constriction 38. Therefore, the pressurecontrol chamber 36 is filled with fuel.

When the fuel overflow port 41 is closed by the overflow control valve40, as shown in FIG. 2, the needle valve 31 sits on the valve seat 30.Therefore, the fuel injection is stopped. At this time, the nozzlechamber 34 and the pressure control chamber 36 become the same fuelpressure. When the overflow control valve 40 opens, that is, it opensthe fuel overflow port 41, the high pressure fuel in the pressurecontrol chamber 36 flows out through a constriction 39 from the fueloverflow port 41 and therefore the pressure in the pressure controlchamber 36 gradually flows. When the pressure in the pressure controlchamber 36 falls, the needle valve 31 rises and the injection of thefuel from the injection port 33 is started.

That is, the pressure control chamber 36 and the fuel overflow port 41are provided between them with a constriction 39. Further, due to otherdelay elements, the injection of fuel is started a little while afterthe overflow control valve 40 opens. Next, when the overflow controlvalve 40 closes, that is, it closes the fuel overflow port 41, the fuelsupplied through the constriction 38 to the inside of the pressurecontrol chamber 36 causes the pressure in the pressure control chamber36 to gradually increase and therefore the fuel injection is stopped alittle while after the overflow control valve 40 closes.

In the present invention, fuel is injected from each fuel injector atleast two times, a prior injection and a later injection, during onecycle of the engine. FIGS. 3A and 3B show two representative fuelinjection methods. FIG. 3A shows the case of performing a pilotinjection P before a main injection M. In this case, the pilot injectionP is the prior injection and the main injection M is the laterinjection.

On the other hand, FIG. 3B shows the case of performing a plurality ofpilot injections P₁, P₂ before the main injection M and performing aplurality of post injections P₃ P₄ after the main injection M. In thiscase, if making the pilot injection P₂ the later injection, the pilotinjection P₁ becomes the prior injection. If making the main injection Mthe later injection, the pilot injections P₁, P₂ become the priorinjections. If making the pilot injection P₃ the later injection, thepilot injections P₁, P₂ and the main injection M become the priorinjections.

Note that the present invention will be explained taking as an examplethe case of performing the pilot injection P before the main injection Mas shown in FIG. 3A.

In the embodiment of the present invention, the target total injectionamount QT is stored in advance in the ROM 22 in the form of a map as afunction of the depression of the accelerator pedal 17, that is, theaccelerator opening degree L, and the engine speed N as shown in FIG.4A. Further, the target main injection amount QM is stored in advance inthe ROM 22 in the form of a map as a function of the total injectionamount QT and the engine speed N as shown in FIG. 4B. On the other hand,the target pilot injection amount QP is obtained by subtracting from thetotal injection amount QT the main injection amount QM.

Further, the injection start timing θM of the main injection M is storedin advance in the ROM 22 in the form of a map as a function of the totalinjection amount QT and the engine speed N as shown in FIG. 5A. Further,the time interval from when the prior injection is performed to when thelater injection is performed is set in advance. In this embodiment ofthe present invention, the time interval TI from when the pilotinjection P is started to when the main injection M is started is storedin advance in the ROM 22 in the form of a map as a function of the totalinjection amount QT and the engine speed N as shown in FIG. 5B. Theinjection start timing OP of the pilot injection P is calculated fromthe injection start timing θM of the main injection M and the timeinterval TI.

Further, in this embodiment of the present invention, the target railpressure in the common rail 13 is set in advance. This target railpressure generally speaking becomes higher the greater the totalinjection amount QT.

Now, when the needle valve 31 opens and the fuel injection is started inFIG. 2, the pressure in the nozzle chamber 34 rapidly drops. If thepressure in the nozzle chamber 34 rapidly drops in this way, a pressurewave is produced. This pressure wave propagates through the inside ofthe high pressure line 35 toward the common rail 13. Next, this pressurewave is reflected at the open end of the high pressure line 35 leadingtoward the inside of the common rail 13. Next, this pressure waveproceeds through the high pressure line 35 toward the nozzle chamber 34in the state with the pressure inverted with respect to the meanpressure, that is, in the form of a high pressure wave, and causes thenozzle chamber 34 to become high in pressure temporarily. For example,if pilot injection has been performed, for a little while after that,the inside of the nozzle chamber 34 becomes temporarily a high pressuredue to the reflected wave in the common rail 13.

On the other hand, when the needle valve 31 closes, the flow of the fuelis rapidly blocked, so the pressure inside the nozzle chamber 34temporarily rises and a pressure wave is formed. This pressure wave alsopropagates through the inside of the high pressure line 35, is reflectedat the common rail 13, and returns to the inside of the nozzle chamber34.

Further, the opening and closing operation of the overflow control valve40 also causes generation of a pressure wave propagated through theinside of the nozzle chamber 34. That is, if the overflow control valve40 opens, the pressure at the fuel overflow port 41 rapidly falls, so apressure wave is generated. If the overflow control valve 40 closes, thepressure of the fuel overflow port 41 rapidly rises, so a pressure waveis generated. These pressure waves pass through the pair ofconstrictions 39, 38 to be propagated through the nozzle chamber 34 andcause the pressure in the nozzle chamber 34 to rise or fall.Simultaneously, the pressure waves are reflected in the nozzle chamber34 and are propagated toward the common rail 13 or the fuel overflowport 41.

In this way, if pilot injection P is performed, the pressure wavesgenerated due to the opening and closing operation of the needle valve31 and the opening and closing operation of the overflow control valve40 cause the fuel pressure in the nozzle chamber 34 to pulsate. Next,main injection M is performed when the fuel pressure in the nozzlechamber 34 is pulsating in this way. However, if main injection M isperformed when the fuel pressure in the nozzle chamber 34 is pulsatingin this way, the injection amount will increase when the fuel pressurein the nozzle chamber 34 becomes higher and the injection amount willdecrease when the fuel pressure in the nozzle chamber 34 becomes lower,so the injection amount of the main injection M will fluctuate.

Next, the fluctuation amount of the injection amount of the maininjection M will be explained with reference to FIGS. 6A to 6B and FIGS.7A to 7C. In FIGS. 6A to 6B and FIGS. 7A to 7C, the abscissa Ti showsthe time interval (msec) from when the pilot injection P was started towhen the main injection M is started, while the ordinate dQ shows thefluctuation amount (mm³) of the injection amount of the main injection Mwith respect to the target value. In FIGS. 6A to 6B and FIGS. 7A to 7C,the □ marks show when the rail pressure is 48 MPa, the o marks show whenthe rail pressure is 80 MPa, and the Δ marks show when the rail pressureis 128 MPa. Note that FIG. 6A to FIG. 6C show when the main injectionamount is small, while FIGS. 7A to 7C show when the main injectionamount is large.

Specifically, FIGS. 6A to 6C show when the pilot injection amount is 2(mm³) and the main injection amount is 2 (mm³), while FIGS. 7A to 7Cshow when the pilot injection amount is 2 (mm³) and the main injectionamount is 20 (mm³).

Now, FIG. 6A and FIG. 7A show the actual fluctuation amount dQ of theinjection amount of the main injection M with respect to the targetvalue for three different rail pressures. As explained above, if thefuel pressure in the nozzle chamber 34 becomes higher, the maininjection amount increases, while if the fuel pressure in the nozzlechamber 34 becomes lower, the main injection amount decreases, so it islearned from FIG. 6A and FIG. 7A that after the pilot injection, thefuel pressure in the nozzle chamber 34 repeatedly rises and falls, thatis, pulsates.

However, looking at FIG. 6A and FIG. 7A, it will be understood that thefluctuation patterns of the main injection amounts expressed by thecurves differ in period, that is, the higher the rail pressure, theshorter the period, but rise and fall by similar forms. As explainedabove, the fuel pressure in the nozzle chamber 34 fluctuates due to thepressure wave propagated between the nozzle chamber 34 and common rail13 or between the nozzle chamber 34 and the fuel overflow port 41. Thedistance between the nozzle chamber 34 and the common rail 13 is a fixedlength and the distance between the nozzle chamber 34 and fuel overflowport 41 is also a fixed length, so if the propagation speed of thepressure wave is constant, the fuel pressure generated in the nozzlechamber 34 after the pilot injection P is performed will pulsate by aset fluctuation pattern.

However, the propagation speed of a pressure wave changes depending onthe fuel pressure and fuel temperature. That is, the propagation speedof the pressure wave is expressed by the square root of (E/γ)·g where Eis the volume elasticity, γ is the density of the fuel, and g is theacceleration of gravity. That is, the propagation speed of the pressurewave is proportional to the square root of the volume elasticity E.However, the volume elasticity E is proportional to the fuel pressureand inversely proportional to the fuel temperature. Therefore, thepropagation speed of the pressure wave becomes faster the higher thefuel pressure and becomes slower the higher the fuel temperature. Thatis, the propagation speed of the pressure wave becomes faster the higherthe rail pressure.

Therefore, when the rail pressure becomes higher, the period offluctuation of the fuel pressure in the nozzle chamber 34 becomesshorter. At this time, the fuel pressure in the nozzle chamber 34fluctuates in a form with the fluctuation pattern contracted in theabscissa direction in FIG. 6A and FIG. 7A, that is, in the time intervalaxis direction. Therefore, as shown in FIG. 6A and FIG. 7A, the higherthe rail pressure, the more the injection amount dQ of the maininjection fluctuates in a form with the fluctuation pattern contractedin the time interval axis direction.

If making the rail pressure 80 MPa shown by the o marks in FIG. 6A andFIG. 7A the reference rail pressure and making the fluctuation patternof the fluctuation amount dQ of the main injection at the time of thisreference rail pressure the reference fluctuation pattern, at the timeof the rail pressure 48 MPa shown by the □ marks, that is, when the railpressure is lower than the reference rail pressure, if the overallfluctuation pattern of the fluctuation amount dQ of the main injectionis uniformly contracted in the time interval axis direction using thetime interval Ti=0 as the fixed point, the timing of upward and downwardfluctuation of the fluctuation pattern will match the timing of upwardand downward fluctuation of the reference fluctuation pattern. At thetime of the rail pressure 128 MPa shown by the Δ marks, that is, whenthe rail pressure is higher than the reference rail pressure, if theoverall fluctuation pattern of the fluctuation amount dQ of the maininjection is uniformly expanded in the time interval axis directionusing the time interval Ti=0 as the fixed point, the timing of upwardand downward fluctuation of the fluctuation pattern will match thetiming of upward and downward fluctuation of the reference fluctuationpattern. FIG. 6B and FIG. 7B show the case when making the fluctuationpattern contract when the rail pressure is 48 MPa and making thefluctuation pattern expand when the rail pressure is 128 MPa so that theperiod of upward and downward fluctuation of the fluctuation patternmatches the period of upward and downward fluctuation of the referencefluctuation pattern in this way.

When the main injection amount is small as shown in FIG. 6B, the rate ofthe deviation between the reference fluctuation pattern and thecontracted or expanded other fluctuation patterns is great, while whenthe main injection amount is large as shown in FIG. 7B, the rate of thedeviation between the reference fluctuation pattern and the contractedor expanded other fluctuation patterns becomes considerably small.Therefore, when the main injection amount is great as shown in FIG. 7B,if making the fluctuation pattern at each rail pressure contract orexpand, it is possible to overlay each fluctuation pattern on thereference fluctuation pattern. That is, it becomes possible tostandardize each fluctuation pattern to a common reference fluctuationpattern.

When it is possible to standardize each fluctuation pattern to a commonfluctuation pattern in this way, it is possible to modify the timeinterval by the contraction rate or expansion rate of each fluctuationpattern and use the modified time interval to find the fluctuationamount dQ of the main injection at each rail pressure from the commonreference fluctuation pattern.

For example, if making the fluctuation pattern of the fluctuation amountdQ of the main injection when the rail pressure is 80 MPa in FIG. 7A thecommon reference fluctuation pattern, the fluctuation amount dQ of themain injection at each time interval Ti when the rail pressure is 48 MPamatches with the reference fluctuation amount dQ of the main injectionat the reference fluctuation pattern when contracting the time intervalTi by the contraction rate of the fluctuation pattern at the time of 48MPa. That is, the contraction rate or expansion rate of the fluctuationpattern at each rail pressure is multiplied with the time interval Ti toobtain the modified time interval. The reference fluctuation amount dQat the reference fluctuation pattern in accordance with that modifiedtime interval matches with the fluctuation amount dQ of the maininjection at each rail pressure. If using the modified time interval inthis way, if storing only the reference fluctuation amount dQ of themain injection at the reference fluctuation pattern, it is possible tofind the fluctuation amount dQ of the main injection at each railpressure from this reference fluctuation amount dQ.

That is, in the present invention, the reference fluctuation amount ofthe later injection, changing along with the reference fluctuationpattern along with an increase in the time interval Ti when the railpressure is a predetermined reference rail pressure, is stored inadvance. Further, the contraction rate or expansion rate of thefluctuation pattern when contracting or expanding the fluctuationpattern of the fluctuation amount of the later injection to overlay iton the reference fluctuation pattern when the rail pressure is not thereference rail pressure is stored in advance. Using the contraction rateor expansion rate, the fluctuation amount of the later injection inaccordance with the rail pressure is calculated from the referencefluctuation amount and time interval Ti.

Specifically speaking, the reference fluctuation amount dQ of the laterinjection at the reference rail pressure is stored in advance as afunction of the time interval Ti. The contraction rate or expansion rateof each fluctuation pattern when overlaying the fluctuation pattern at arepresentative rail pressure on the reference fluctuation pattern isstored in advance. By multiplying the contraction rate or expansion rateof the fluctuation pattern at the current rail pressure with the timeinterval Ti, the modified time interval is found. The referencefluctuation amount dQ of the later injection in accordance with thismodified time interval is made the fluctuation amount of the laterinjection at the current rail pressure.

Next, various embodiments based on this basic thinking of the presentinvention will be successively explained.

As shown in FIG. 6B and FIG. 7B, the fluctuation amount dQ of the maininjection at the same time interval Ti becomes greater the higher therail pressure. Therefore, to standardize the fluctuation pattern at eachrail pressure to the common reference fluctuation pattern, it ispreferable to contract or expand the fluctuation pattern at each railpressure in accordance with the rail pressure in the ordinate directionof FIG. 6B and FIG. 7B, that is, in the direction increasing ordecreasing the fluctuation amount dQ of the main injection. FIG. 6C andFIG. 7C show the case of contracting or expanding the fluctuationpattern at each rail pressure in the direction increasing or decreasingthe fluctuation amount dQ of the main injection to overlay it on thereference fluctuation pattern.

In this embodiment of the present invention, the contraction rate orexpansion rate of the fluctuation pattern when contracting or expandingthe fluctuation pattern of the fluctuation amount of the later injectionto overlay it on the reference fluctuation pattern is stored for eachrail pressure. In FIG. 6B and FIG. 7B, by multiplying the referencefluctuation amount dQ when the rail pressure is 80 MPa with thereciprocal of the contraction rate or reciprocal of the expansion rate,the fluctuation amount dQ of the main injection at each rail pressure iscalculated.

Expressed in general terms, in this embodiment of the present invention,the contraction rate or expansion rate of the fluctuation pattern ateach rail pressure is comprised of a first contraction rate or firstexpansion rate in a direction increasing or decreasing the time intervalTi and a second contraction rate or second expansion rate in a directionincreasing or decreasing the fluctuation amount dQ of the injectionamount. These second contraction rate and second expansion rate arefunctions of the rail pressure. When the rail pressure is not thereference rail pressure, the time interval is multiplied with the firstcontraction rate or first expansion rate to find the modified timeinterval, and the reference fluctuation amount dQ in accordance withthis modified time interval Ti is multiplied with the reciprocal of thesecond contraction rate or the reciprocal of the second expansion rateand the obtained amount is made the fluctuation amount of the laterinjection.

FIG. 8A shows the fluctuation amount dQ of the main injection whenmaking the injection amount of the main injection 5 (mm³), 10 (mm³), 20(mm³), 30 (mm³), and 40 (mm³) in the state maintaining the rail pressureat 48 MPa. Even when the time interval Ti is the same, if thefluctuation amount of the main injection changes, that is, the injectiontiming changes, the region of the fluctuation pattern affecting theinjection changes, so the fluctuation amount dQ of the main injectionchanges in accordance with the fluctuation amount of the main injection.In this case, the fluctuation amount dQ of the main injection at thesame time interval Ti generally speaking becomes larger the greater theinjection amount of the main injection. Therefore, to standardize thefluctuation pattern at each rail pressure to the common referencefluctuation pattern, it is preferable to contract or expand thefluctuation pattern at each rail pressure in the ordinate direction ofFIG. 8A, that is, in the direction increasing or decreasing thefluctuation amount dQ of the main injection, in accordance with the railpressure. FIG. 8B shows the case of contracting or expanding thefluctuation pattern at each rail pressure in the direction increasing ordecreasing the fluctuation amount dQ of the main injection to overlay iton the reference fluctuation pattern.

In this case, in this embodiment of the present invention, thecontraction rate or expansion rate of the fluctuation pattern whencontracting or expanding the fluctuation pattern of the fluctuationamount of the later injection to overlay it on the reference fluctuationpattern is stored for each injection amount of the main injection. InFIG. 8B, by multiplying the reference fluctuation amount dQ when theinjection amount is 20 (mm³) with the reciprocal of the contraction rateor reciprocal of the expansion rate, the fluctuation amount dQ of themain injection is calculated.

Expressed in general terms, in this embodiment of the present invention,the contraction rate or expansion rate of the fluctuation pattern ateach rail pressure is comprised of a first contraction rate or firstexpansion rate in a direction increasing or decreasing the time intervalTi and a second contraction rate or second expansion rate in a directionincreasing or decreasing the fluctuation amount dQ of the injectionamount. These second contraction rate and second expansion rate arefunctions of the injection amount of the main injection. When the railpressure is not the reference rail pressure, the time interval ismultiplied with the first contraction rate or first expansion rate tofind the modified time interval, the reference fluctuation amount dQ inaccordance with this modified time interval Ti is multiplied with thereciprocal of the second contraction rate or the reciprocal of thesecond expansion rate, and the obtained amount is made the fluctuationamount of the later injection.

Further, while not shown, when the pilot injection amount changes, thefluctuation amount dQ of the main injection changes. Therefore, in thiscase as well, to standardize the fluctuation pattern at each pilotinjection amount to the common reference fluctuation pattern, it ispreferable to contract or expand the fluctuation pattern at each pilotinjection amount in the direction increasing or decreasing thefluctuation amount dQ of the main injection. In this case, expressed ingeneral terms, the contraction rate or expansion rate of the fluctuationpattern at each rail pressure is comprised of a first contraction rateor first expansion rate in a direction increasing or decreasing the timeinterval Ti and a second contraction rate or second expansion rate in adirection increasing or decreasing the fluctuation amount dQ of theinjection amount. These second contraction rate and second expansionrate are functions of the injection amount of the pilot injectionamount. When the rail pressure is not the reference rail pressure, thetime interval is multiplied with the first contraction rate or firstexpansion rate to find the modified time interval, the referencefluctuation amount dQ in accordance with this modified time interval Tiis multiplied with the reciprocal of the second contraction rate or thereciprocal of the second expansion rate, and the obtained amount is madethe fluctuation amount of the later injection.

Next, an example of the fuel injection control for controlling the fuelinjection to a target value will be explained with reference to the fuelinjection control routine shown in FIG. 9.

Referring to FIG. 9, first, at step 100, the total injection amount QTis calculated from the map shown in FIG. 4A. Next, at step 101, the maininjection amount QM is calculated from the map shown in FIG. 4B. Next,at step 102, the total injection amount QT is subtracted by the maininjection amount QM to calculate the pilot injection amount QP. Next, atstep 103, the main injection start timing θM is calculated from the mapshown in FIG. 5A. Next, at step 104, the time interval TI is calculatedfrom the map shown in FIG. 5B. Next, at step 105, the pilot injectionstart timing θP is calculated from the main injection start timing θMand the time interval TI.

Next, at step 106, the contraction rate or expansion rate K1 whencontracting or expanding the fluctuation pattern of the fluctuationamount dQ of the main injection amount in a direction increasing orreducing the time interval in accordance with the rail pressure based onthe rail pressure detected by the fuel pressure sensor 16 or the meanvalue of the rail pressure in a fixed time (hereinafter referred tosimply as the “rail pressure”) to overlay it on the referencefluctuation pattern is calculated. This contraction rate or expansionrate K1 is shown in FIG. 10A. If the reference rail pressure is 80 MPa,when the rail pressure is near 80 MPa, the contraction rate or expansionrate K1 is 1.0. As the rail pressure becomes lower than the referencerail pressure, K1 decreases, that is, the fluctuation pattern contracts,while as the rail pressure becomes higher than the reference railpressure, K1 increases, that is, the fluctuation pattern is expanded.

Next, at step 107, the contraction rate or expansion rate K1 of thefluctuation pattern is multiplied with the time interval TI so as tocalculate the modified time interval Ti. Next, at step 108, if thereference rail pressure is made 80 MPa, the reference main injectionamount QM is made 20 (mm³), and the reference pilot injection amount QPis made 2 (mm³), that is, the fluctuation amount shown by the o marks inFIG. 7B is made the reference fluctuation amount dQ, the referencefluctuation amount dQ in accordance with the modified time interval Tiis calculated.

Next, at step 109, the contraction rate or expansion rate K2 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the main injection amount in a direction increasing orreducing the fluctuation amount of the main injection in accordance withthe rail pressure to overlay it on the reference fluctuation pattern iscalculated. The change of K2 is shown in FIG. 10B. As shown in FIG. 10B,near the rail pressure serving as the reference, the value of K2 becomes1.0. When the rail pressure becomes lower than the reference railpressure, the value of K2 becomes larger than 1.0, while when the railpressure becomes higher than the reference rail pressure, the value ofK2 becomes smaller than 1.0.

Next, at step 110, the contraction rate or expansion rate K3 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the main injection amount in a direction increasing orreducing the fluctuation amount of the main injection in accordance withthe main injection amount QM to overlay it on the reference fluctuationpattern is calculated. This change of K3 is shown in FIG. 10C. As shownin FIG. 10C, near the main injection amount serving as the reference,the value of K3 becomes 1.0. When the main injection amount becomeslower than the reference main injection amount, the value of K3 becomeslarger than 1.0, while when the main injection amount becomes higherthan the reference main injection amount, the value of K3 becomessmaller than 1.0.

Next, at step 111, the contraction rate or expansion rate K4 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the main injection amount in a direction increasing orreducing the fluctuation amount of the main injection in accordance withthe pilot injection amount to overlay it on the reference fluctuationpattern is calculated. This change of K4 is shown in FIG. 10D. As shownin FIG. 10D, near the pilot injection amount serving as the reference,the value of K4 becomes 1.0. When the pilot injection amount becomeslower than the reference pilot injection amount, the value of K4 becomeslarger than 1.0, while when the pilot injection amount becomes higherthan the reference pilot injection amount, the value of K4 becomessmaller than 1.0.

Next, at step 112, the reference fluctuation amount dQ calculated atstep 108 is multiplied with the reciprocal of the contraction rates orexpansion rates K2, K3, and K4 to calculate the final fluctuation amountdQ of the main injection. Next, at step 113, a command value of the maininjection is corrected so that the actual injection amount becomes thetarget value based on this fluctuation amount dQ. For example, when thefluctuation amount dQ is plus, the command value of the main injectionis corrected so that the main injection amount QM calculated at step 101is reduced by the fluctuation amount dQ and the actual injection amountbecomes the reduced main injection amount (QM−dQ). As opposed to this,if the fluctuation amount dQ is minus, the command value of the maininjection is corrected so that the main injection amount QM is increasedby the fluctuation amount dQ and the actual injection amount becomes theincreased main injection amount (QM+dQ). In this way, the actualinjection amount is controlled to the target value QT. Next, at step114, the processing for injection of the pilot injection and maininjection is performed.

Now, as explained above, the main injection amount fluctuates due to thepressure pulsation occurring in the nozzle chamber 34, but this maininjection amount also fluctuates due to the fluctuation of the openingtiming of the needle valve 31. That is, based on the command forstarting the main injection, the overflow control valve 40 opens, thefuel pressure in the pressure control chamber 36 gradually falls, andthe needle valve 31 opens when the pressure difference between theneedle chamber 34 and the pressure control chamber 36 becomes at least afixed pressure. In this case, when the fuel pressure in the pressurecontrol chamber 36 gradually falls, if the pressure pulsation causes thefuel pressure in the nozzle chamber 34 to rapidly rise or the fuelpressure in the pressure control chamber 36 to rapidly fall, thepressure difference between the needle chamber 34 and the pressurecontrol chamber 36 will become at least a fixed value. Therefore, theopening timing of the needle valve 31 will be advanced. As opposed tothis, when the fuel pressure in the pressure control chamber 36gradually falls, if the pressure pulsation causes the fuel pressure inthe nozzle chamber 34 to rapidly fall or the fuel pressure in thepressure control chamber 36 to rapidly rise, time will be required untilthe pressure difference between the needle chamber 34 and the pressurecontrol chamber 36 becomes at least a fixed value, so the opening timingof the needle valve 31 is delayed.

In this way, the opening timing of the needle valve 31 fluctuates inaccordance with the rate of change of the pressure pulsation, that is,the differentiated value of the change of the pressure pulsation. Inthis case, if the opening timing of the needle valve 31 is advanced, themain injection amount will increase, while if the opening timing of theneedle valve 31 is delayed, the main injection amount will decrease.Therefore, if the opening timing of the needle valve 31 fluctuates dueto the effect of the rate of change of the pressure pulsation, the maininjection amount will fluctuate along with this.

In this way, the main injection amount fluctuates due to both thefluctuation of the injection amount due to fluctuation of the fuelpressure in the nozzle chamber 34 and fluctuation of the fluctuationamount due to fluctuation in the opening timing of the needle valve 31.However, the injection amount when the needle valve 31 opens isdetermined by the fuel pressure in the suck chamber 32. As shown in FIG.7, when the main injection amount is large, the lift of the needle valve31 becomes large and therefore at this time the fuel pressure in thesuck chamber 32 pulsates along with the fuel pressure in the nozzlechamber 34. That is, when the main injection amount is large, ifpulsation occurs in the nozzle chamber 34, the main injection amountwill fluctuate. That is, the fluctuation amount dQ of the main injectionamount shown in FIG. 7 includes both the fluctuation amount of theinjection amount due to pulsation in the nozzle chamber 34 and thefluctuation amount of the injection amount due to fluctuation of theopening timing of the needle valve 31.

On the other hand, when the main injection amount is small such as shownin FIG. 6, the lift of the needle valve 31 is small. At this time, thepressure pulsation occurring in the nozzle chamber 32 does not propagatemuch at all in the suck chamber 32. Therefore, when main injectionamount is small, there is not that much fluctuation in the injectionamount due to pressure pulsation of the nozzle chamber 34, that is,pressure pulsation in the suck chamber 32. At this time, the fluctuationof the main injection amount due to fluctuation of the opening timing ofthe needle valve 31 becomes dominant.

However, the fluctuation in the main injection due to pressure pulsationin the nozzle chamber 32 is due to the magnitude of the absolutepressure in the nozzle chamber 32. The fluctuation in the opening timingof the needle valve 31 is not due to the magnitude of the absolutepressure in the nozzle chamber 34, but is due to the rate of change ofthe fuel pressure in the nozzle chamber 34 or pressure control chamber36. Therefore, the fluctuation pattern of the fluctuation amount dQ ofthe main injection amount shown in FIGS. 6A to 6C where the fluctuationof the opening timing of the needle valve 31 dominates the fluctuationof the main injection amount and the fluctuation pattern of thefluctuation amount dQ of the main injection amount shown in FIGS. 7A to7C where both the effect due to the pressure pulsation in the nozzlechamber 34 and the effect due to the fluctuation of the opening timingof the needle valve 31 appear differ somewhat.

Therefore, when making the fluctuation patterns shown in FIGS. 7A to 7Ccontract or expand, these fluctuation patterns will generally overlaythe fluctuation patterns shown in FIGS. 6A to 6C, but will notaccurately overlay them. Therefore, to make the injection amount matchthe target value more accurately, it is preferable to provide two maps,that is, the map of the fluctuation amount dQ of the main injectionstandardized as shown in FIG. 6C for when the fuel injection amount issmall and the map of the fluctuation amount dQ of the main injectionstandardized as shown in FIG. 7C for when the fuel injection amount islarge, and, when finding the fluctuation amount dQ of the maininjection, to selectively use one of these two maps in accordance withthe fuel injection amount.

On the other hand, when the prior injection is pilot injection with asmall injection amount, the fluctuation amount dQ of the main injectionfluctuates by a fluctuation pattern as shown in FIG. 6A to FIG. 8B, butwhen the injection amount of the prior injection is large as shown by Mof FIG. 3B, the fluctuation amount dQ of the later injection willfluctuate by a considerably different fluctuation pattern from thefluctuation pattern shown in FIG. 6A to FIG. 8C. Therefore, when thereare cases where the injection amounts of the prior injection are smalland large as shown in FIG. 3B, it is preferable to provide four maps,that is, the map of the fluctuation amount dQ of the later injectionstandardized for when the injection amount of the prior injection issmall and the injection amount of the later injection is small, the mapof the fluctuation amount dQ of the later injection standardized forwhen the injection amount of the prior injection is small and theinjection amount of the later injection is large, the map of thefluctuation amount dQ of the later injection standardized for when theinjection amount of the prior injection is large and the injectionamount of the later injection is small, and the map of the fluctuationamount dQ of the later injection standardized for when the injectionamount of the prior injection is large and the injection amount of thelater injection is large, and, when finding the fluctuation amount dQ ofthe later injection, to selectively use one of these four maps inaccordance with the injection amount of the prior injection and theinjection amount of the later injection.

Next, an embodiment separately finding the fluctuation in the openingtiming of the needle valve 31 and the fluctuation in the injectionamount of the main injection due to the fluctuation of the injectionpressure and controlling the injection amount to the target value basedon these fluctuations will be explained.

As explained above, the fluctuation pattern of the fluctuation amount dQof the main injection amount shown in FIGS. 6A to 6C where thefluctuation of the opening timing of the needle valve 31 dominates thefluctuation of the main injection amount and the fluctuation pattern ofthe fluctuation amount dQ of the main injection amount shown in FIGS. 7Ato 7C where both the effect due to the pressure pulsation in the nozzlechamber 34 and the effect due to the fluctuation of the opening timingof the needle valve 31 appear differ somewhat. Therefore, when makingthe fluctuation patterns shown in FIGS. 7A to 7C contract or expand,these fluctuation patterns will generally overlay the fluctuationpatterns shown in FIGS. 6A to 6C, but will not accurately overlay them.

However, when taking out only the fluctuation of the opening timing ofthe needle valve 31, by making the fluctuation patterns at the differentrail pressures contract or expand, it is possible to overlay thefluctuation patterns on a fluctuation pattern serving as a singlereference. If taking out only the fluctuation of the main injectionamount minus the fluctuation of the main injection amount due tofluctuation of the opening timing of the needle valve 31, in this caseas well, by making the fluctuation patterns at the different railpressures contract or expand, it is possible to overlay the fluctuationpatterns on a fluctuation pattern serving as a single reference.Therefore, it is possible to make the injection amount accurately matchwith the target value.

Next, this will be explained while referring to FIGS. 11A to 11C andFIGS. 12A to 12C.

FIGS. 11A to 11C show the relationship between the time interval Ti(msec) and the fluctuation amount Δτ (μsec) of the opening timing of theneedle valve 31. Further, FIGS. 11A to 11C show the case where the pilotinjection amount is 2 (mm³). The □ marks show when the rail pressure is48 MPa, the o marks show when the rail pressure is 80 MPa, and the Δmarks show when the rail pressure is 128 MPa.

FIG. 11A shows the actual value of the fluctuation amount Δτ of theopening timing of the needle valve 31 at each rail pressure. FIG. 11Bshows the case when making the rail pressure 80 MPa the reference railpressure, making the fluctuation pattern of the opening timing of theneedle valve 31 at this time the reference fluctuation pattern, andcontracting or expanding the fluctuation pattern when the rail pressureis 48 MPa and 128 MPa shown in FIG. 11A in the time interval axisdirection so that the period of upward and downward fluctuation of thefluctuation patterns match the period of upward and downward fluctuationof the reference fluctuation pattern.

On the other hand, FIG. 11C shows the case when contracting or expandingthe fluctuation patterns when the rail pressure is 48 MPa and 128 MPashown in FIG. 11B in the vertical direction, that is, the directionincreasing or decreasing the fluctuation amount Δτ of the opening timingof the needle valve 31, so that these fluctuation patterns overlay thereference fluctuation pattern. If taking out the fluctuation amount Δτof the opening timing of the needle valve 31 in this way, it is learnedthat it is possible to standardize the fluctuation pattern as shown inFIG. 11C.

Note that the fluctuation amount ΔQm of the main injection when theopening timing of the needle valve 31 fluctuates by a unit time becomesgreater the higher the rail pressure. The fluctuation amount ΔQm of themain injection is found in advance by experiments. Therefore, when theopening timing of the needle valve 31 fluctuates by the Δτ time, bymultiplying ΔQm with Δτ, it is possible to find the fluctuation amountdQm of the main injection (=ΔQm·Δτ).

FIGS. 12A and 12B show the relationship between the time interval Ti andthe fluctuation amount dQt (mm³) of the main injection due to theeffects of only the fluctuation of the injection pressure obtained bysubtracting from the actual fluctuation amount dQ (mm³) of the maininjection the fluctuation amount dQm of the main injection due tofluctuation of the opening timing of the needle valve 31. Further, FIGS.12A and 12B show the case where the pilot injection amount is 2 (mm³)and the rail pressure is the reference rail pressure 80 MPa. The + marksshow when the main injection amount is 5 (mm³), the ⋄ marks show whenthe main injection amount is 10 (mm³), the Δ marks show when the maininjection amount is 20 (mm³), o marks show when the main injectionamount is 30 (mm³), and the □ marks show when the main injection amountis 40 (mm³).

FIG. 12A shows the fluctuation amount dQt of the main injection at eachmain injection amount when the rail pressure is the reference railpressure 80 MPa. FIG. 12B shows the case of making the fluctuationpattern when the rail pressure is the standard rail pressure 80 MPa andthe main injection amount is 20 (mm³) the reference fluctuation patternand contracting or expanding the fluctuation patterns at the time of themain injection amounts of 5 (mm³), 10 (mm³), 30 (mm³), and 40 (mm³) inthe vertical direction, that is, the direction increasing or decreasingthe fluctuation amount dQt of the main injection, so that thefluctuation patterns overlay the reference fluctuation pattern. Iftaking out the fluctuation amount dQt of the main injection due to justfluctuation of the injection pressure, it is possible to standardize thefluctuation pattern as shown in FIG. 12B.

Note that in FIG. 12A, when the main injection amount is small such as 5(mm³) (+ marks) or 10 (mm³) (⋄marks), the lift of the needle valve 31 issmall, so the fuel pressure in the suck chamber 32 will not fluctuatethat much and therefore the fluctuation amount dQt of the main injectionwill be small. Even when the fluctuation amount dQt of the maininjection is small in this way, if the fluctuation pattern is expandedin the vertical direction, it will overlay the reference fluctuationpattern.

In this embodiment, there are two fuel injection control methods. Thefirst fuel injection control method is the method of finding thefluctuation amount Δτ of the opening timing of the needle valve 31 fromFIG. 11C, controlling the opening timing of the needle valve 31 to thetarget value by this fluctuation amount Δτ, finding the fluctuationamount dQt of the main injection from FIG. 12B, and controlling theinjection amount of the main injection to the target value by thisfluctuation amount dQt, while the second fuel injection control methodis the method of finding the fluctuation amount Δτ of the opening timingof the needle valve 31 from FIG. 11C, finding the fluctuation amount dQm(=ΔQm·Δτ) of the main injection due to the fluctuation in the openingtiming of the needle valve 31 from this fluctuation amount Δτ, findingthe fluctuation amount dQt of the main injection from FIG. 12B, andcontrolling the fluctuation amount of the main injection to the targetvalue by this fluctuation amount dQt and the fluctuation amount dQm ofthe main injection due to fluctuation of the opening timing of theneedle valve 31.

FIG. 13 and FIG. 14 shows a fuel injection control routine for executingthe first fuel injection control method.

Referring to FIG. 13 and FIG. 14, first, at step 200, the totalinjection amount QT is calculated from the map shown in FIG. 4A. Next,at step 201, the main injection amount QM is calculated from the mapshown in FIG. 4B. Next, at step 202, the total injection amount QT issubtracted by the main injection amount QM to calculate-the pilotinjection amount QP. Next, at step 203, the main injection start timingθM is calculated from the map shown in FIG. 5A. Next, at step 204, thetime interval TI is calculated from the map shown in FIG. 5B. Next, atstep 205, the pilot injection start timing θP is calculated from themain injection start timing θM and the time interval TI.

Next, at step 206, the contraction rate or expansion rate IK1 whencontracting or expanding the fluctuation pattern of the fluctuationamount Δτ of the opening timing of the needle valve 21 in a directionincreasing or reducing the time interval in accordance with the railpressure to overlay it on the reference fluctuation pattern iscalculated. This contraction rate or expansion rate IK1 is shown in FIG.15A. If the reference rail pressure is 80 MPa, when the rail pressure isnear 80 MPa, the contraction rate or expansion rate IK1 is 1.0. As therail pressure becomes lower than the reference rail pressure, IK1decreases, that is, the fluctuation pattern contracts, while as the railpressure becomes higher than the reference rail pressure, IK1 increases,that is, the fluctuation pattern is expanded.

Next, at step 207, the contraction rate or expansion rate IK1 of thefluctuation pattern is multiplied with the time interval TI so as tocalculate the modified time interval Ti. Next, at step 208, if thereference rail pressure is made 80 MPa and the reference pilot injectionamount QP is made 20 (mm³), that is, if the fluctuation amount At of theopening timing shown by the o marks in FIG. 11B is made the referencefluctuation amount, the reference fluctuation amount of the openingtiming in accordance with the modified time interval Ti is calculated.

Next, at step 209, the contraction rate or expansion rate IK2 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the opening timing in a direction increasing or reducing thefluctuation amount of the opening timing in accordance with the railpressure to overlay it on the reference fluctuation pattern iscalculated. The change of IK2 is shown in FIG. 15B. As shown in FIG.15B, near the rail pressure serving as the reference, the value of IK2becomes 1.0. When the rail pressure becomes lower than the referencerail pressure, the value of IK2 becomes larger than 1.0, while when therail pressure becomes higher than the reference rail pressure, the valueof IK2 becomes smaller than 1.0.

Next, at step 210, the contraction rate or expansion rate IK3 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the opening timing in a direction increasing or reducing thefluctuation amount of the opening timing in accordance with the pilotinjection amount to overlay it on the reference pattern is calculated.This change of IK3 is shown in FIG. 15C. As shown in FIG. 15C, near thepilot injection amount serving as the reference, the value of IK3becomes 1.0. When the pilot injection amount becomes lower than thereference pilot injection amount, the value of IK3 becomes larger than1.0, while when the pilot injection amount becomes higher than thereference pilot injection amount, the value of IK3 becomes smaller than1.0.

Next, at step 211, the reference fluctuation amount Δτ of the openingtiming calculated at step 208 is multiplied with the reciprocal of thecontraction rates or expansion rates IK2 and IK3 to calculate the finalfluctuation amount Δτ of the opening timing. Next, at step 212, acommand value of the opening timing is corrected so that the actualopening timing becomes the target value based on this fluctuation amountΔτ. For example, when the opening timing is plus, the command value ofthe main injection is corrected so that the main injection start timingθM calculated at step 203 is delayed by exactly the fluctuation amountΔτ. On the other hand, if the opening timing is minus, the command valueof the opening timing is corrected so that the main injection starttiming θM calculated at step 203 is advanced by exactly the fluctuationamount Δτ. In this way, the actual opening timing of the needle valve 31at the time of start of the main injection is controlled to the targetvalue θM.

Next, at step 213, the contraction rate or expansion rate FK1 whencontracting or expanding the fluctuation pattern of the fluctuationamount dQ of the main injection in a direction increasing or reducingthe time interval in accordance with the rail pressure to overlay it onthe reference fluctuation pattern is calculated. This contraction rateor expansion rate FK1 is shown in FIG. 16A. If the reference railpressure is 80 MPa, when the rail pressure is near 80 MPa, thecontraction rate or expansion rate FK1 is 1.0. When the rail pressurebecomes lower than the reference rail pressure, FK1 decreases, that is,the fluctuation pattern is contracted, while when the rail pressurebecomes higher than the reference rail pressure, FK1 increases, that is,the fluctuation pattern is expanded.

Next, at step 214, the contraction rate or expansion rate FK1 of thefluctuation pattern is multiplied with the time interval TI to calculatethe modified time interval Ti. Next, at step 215, when the referencerail pressure is made 80 MPa, the main injection amount QM serving as areference is made 20 (mm³), and the pilot injection amount QP serving asa reference is made 2 (mm³), that is, when the fluctuation amount shownby the A marks in FIG. 12B is made the reference fluctuation amount dQ,the reference fluctuation amount dQ corresponding to the modified timeinterval Ti is calculated.

Next, at step 216, the contraction rate or expansion rate FK2 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the main injection amount in a direction increasing orreducing the fluctuation amount of the main injection in accordance withthe rail pressure to overlay it on the reference fluctuation pattern iscalculated. This change of FK2 is shown in FIG. 16B. As shown in FIG.16B, near the rail pressure serving as the reference, the value of FK2becomes 1.0. When the rail pressure becomes lower than the referencerail pressure, the value of FK2 becomes larger than 1.0, while when therail pressure becomes higher than the reference rail pressure, the valueof FK2 becomes smaller than 1.0.

Next, at step 217, the contraction rate or expansion rate FK3 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the main injection amount in a direction increasing orreducing the fluctuation amount of the main injection in accordance withthe main injection amount QM to overlay it on the reference fluctuationpattern is calculated. This change of FK3 is shown in FIG. 16C. As shownin FIG. 16C, near the main injection amount serving as the reference,the value of FK3 becomes 1.0. When the main injection amount becomeslower than the reference main injection amount, the value of FK3 becomeslarger than 1.0, while when the main injection amount becomes higherthan the reference main injection amount, the value of FK3 becomessmaller than 1.0.

Next, at step 218, the contraction rate or expansion rate FK4 of thefluctuation pattern when contracting or expanding the fluctuationpattern of the main injection amount in a direction increasing orreducing the fluctuation amount of the main injection in accordance withthe pilot injection amount to overlay it on the reference fluctuationpattern is calculated. This change of FK4 is shown in FIG. 16D. As shownin FIG. 16D, near the pilot injection amount serving as the reference,the value of FK4 becomes 1.0. When the pilot injection amount becomeslower than the reference pilot injection amount, the value of FK4becomes larger than 1.0, while when the pilot injection amount becomeshigher than the reference pilot injection amount, the value of FK4becomes smaller than 1.0.

Next, at step 219, the reference fluctuation amount dQ calculated atstep 215 is multiplied with the reciprocal of the contraction rates orexpansion rates FK2, FK3, and FK4 to calculate the final fluctuationamount At of the main injection. Next, at step 220, a command value ofthe main injection is corrected so that the actual injection amountbecomes the target value based on this fluctuation amount dQ. Forexample, when the fluctuation amount dQ is plus, the command value ofthe main injection is corrected so that the main injection amount QMcalculated at step 201 is reduced by the fluctuation amount dQ and theactual injection amount becomes the reduced main injection amount(QM−dQ). As opposed to this, if the fluctuation amount dQ is minus, thecommand value of the main injection is corrected so that the maininjection amount QM is increased by the fluctuation amount dQ and theactual injection amount becomes the increased main injection amount(QM+dQ). In this way, the actual injection amount is controlled to thetarget value QT. Next, at step 221, the processing for injection of thepilot injection and main injection is performed.

FIG. 17 and FIG. 18 show a fuel injection control routine for executingthe second fuel injection control method.

In this routine, the only difference from the routine shown in FIG. 13and FIG. 14 is step 212′ and 220′. The rest of the steps 200 to 211, 213to 219, and 221 are the same as steps 200 to 211, 213 to 219, and 221 inFIG. 13 and FIG. 14. Therefore, below, only steps 212′ and 220′ in theroutine shown in FIG. 17 and FIG. 18 will be explained.

As explained above, the fluctuation amount ΔQm for when the openingtiming of the needle valve 31 fluctuates by a unit time is found inadvance by experiments. At step 212′, this ΔQm is multiplied with thefluctuation amount Δτ of the opening timing found at step 211 so as tocalculate the fluctuation amount dQm of the main injection (=Δθm·Δτ).Next, at step 220′, the main injection command value is corrected basedon the fluctuation amount dQm of the main injection and the fluctuationamount dQ of the main injection found at step 219.

In this case, there are various methods for correction of the maininjection command value. The main injection command value is correctedby any of these methods. The simplest method is to add to the maininjection amount QM calculated at step 201 the fluctuation amounts dQand dQm and make the added up main injection amount (QM+dQ+dQm) thefinal main injection amount. The injection start timing is left as itis, while the injection end timing is determined so that the actual maininjection amount becomes the final main injection amount (QM+dQ+dQm).

Further, it is possible to convert the fluctuation amount dQ to theinjection timing Δt and convert the fluctuation amount dQm to theinjection time Δtm and to extend or shorten the injection time byexactly the sum of these calculated fluctuation amounts (Δt+Δtm).Alternatively, it is possible to advance or delay the injection starttiming by exactly the fluctuation amount Δtm and advance or delay theinjection end timing by exactly the fluctuation amount Δt.

1. A fuel injection system of an internal combustion engine providedwith a common rail and fuel injectors connected to the common rail,performing fuel injection from each fuel injector at least the two timesof prior injection and later injection during one cycle of the engine,and changing in fluctuation amount of the later injection with respectto a target value depending on a time interval from when the priorinjection is performed to when the later injection is performed, saidfuel injection system of an internal combustion engine provided with astorage device for storing a reference fluctuation amount of the laterinjection changing along with a reference fluctuation pattern along withan increase in said time interval when the rail pressure is apredetermined reference rail pressure and storing a contraction rate orexpansion rate of the fluctuation pattern when contracting or expandingthe fluctuation pattern of said fluctuation amount of the laterinjection when the rail pressure is not the reference rail pressure tooverlay it on the reference fluctuation pattern, a calculation devicefor using said contraction rate or expansion rate to calculate saidfluctuation amount of the later injection in accordance with the railpressure from said reference fluctuation amount and time interval, and acontrol device for using the fluctuation amount calculated by saidcalculation device to control an injection amount to a target value. 2.A fuel injection system of an internal combustion engine as set forth inclaim 1, wherein when the rail pressure is not the reference railpressure, said calculation device multiples the time interval with thecontraction rate or expansion rate to find a modified time interval andmakes the reference fluctuation amount in accordance with said modifiedtime interval said fluctuation amount of the later injection.
 3. A fuelinjection system of an internal combustion engine as set forth in claim1, wherein said the contraction rate or expansion rate of thefluctuation pattern at each rail pressure stored in said storage deviceis comprised of a first contraction rate or first expansion rate in adirection increasing or decreasing the time interval and a secondcontraction rate or second expansion rate in a direction increasing ordecreasing the fluctuation amount of the injection amount and, when therail pressure is not the reference rail pressure, the time interval ismultiplied with the first contraction rate or first expansion rate tofind a modified time interval, the reference fluctuation amount inaccordance with this modified time interval is multiplied with thereciprocal of the second contraction rate or the reciprocal of thesecond expansion rate, and the obtained amount is made the fluctuationamount of the later injection.
 4. A fuel injection system of an internalcombustion engine as set forth in claim 3, wherein said secondcontraction rate and second expansion rate are functions of the railpressure.
 5. A fuel injection system of an internal combustion engine asset forth in claim 3, wherein said second contraction rate and secondexpansion rate are functions of the injection amount of the laterinjection.
 6. A fuel injection system of an internal combustion engineas set forth in claim 3, wherein said second contraction rate and secondexpansion rate are functions of the injection amount of the priorinjection.
 7. A fuel injection system of an internal combustion engineas set forth in claim 1, wherein the reference fluctuation amount of thelater injection stored in said storage device is comprised of aplurality of sets of reference fluctuation amounts, and the injectionamount is controlled to a target value by selectively using one set ofthe reference fluctuation amounts from the plurality of sets ofreference fluctuation amounts in accordance with the injection amount ofthe prior injection or the injection amount of the later injection.
 8. Afuel injection system of an internal combustion engine as set forth inclaim 1, wherein the reference fluctuation amount of the later injectionstored in said storage device is comprised of a reference fluctuationamount of an opening timing of the fuel injector when the laterinjection is to be performed and a reference fluctuation amount of aninjection amount at the later injection excluding the injection amountdue to the opening timing of the fuel injector, and the injection amountis controlled to a target value based on these reference fluctuationamounts.
 9. A fuel injection system of an internal combustion engine asset forth in claim 8, wherein the opening timing of the fuel injector iscontrolled to a target value based on the reference fluctuation amountof the opening timing of said fuel injector and the injection timing iscontrolled so that the injection amount becomes a target value based onthe reference fluctuation amount of said injection amount.
 10. A fuelinjection system of an internal combustion engine as set forth in claim8, wherein said the fluctuation amount of the later injection based onthe fluctuation of the opening timing of the fuel injector is foundbased on the reference fluctuation amount of the opening timing of thefuel injector, and the injection timing is controlled so that theinjection amount becomes the target value based on the referencefluctuation amount of said injection amount and the fluctuation amountof the injection based on fluctuation of said opening timing.